Process scrubbers are prevalent in chemical industry. In polycarbonate (PC) production, caustic scrubbers are frequently used to remove acidic gases by converting them to salt, water, and carbon dioxide. This is typically done by mixing the acidic effluents from the reactors with caustic in a column via a counter flow system. As the acidic effluents react with the caustic, this operation depletes the caustic strength. To maintain adequate levels of caustic, the concentration of caustic is normally monitored through a manual sampling, and the caustic concentration is determined with a manual acid-base titration. Such caustic strength analysis is typically done on a regular periodicity throughout the day. Depending on the titration results, the caustic concentration can be adjusted by adding fresh caustic solution to the scrubber. A long time period between the manual caustic measurements can result in inefficient operation of the scrubbers and possible process safety issues. Thus, there is a need for a real-time online solution to ensure safe operation and efficient use of caustic. This need and other needs are satisfied by the disclosed invention.